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if you go differential mount the switch on the wall and pipe over to the taps the pump and water in the pipes willl make even more problems...if not on the walll...saw those resistance flow switches were they sense water flow and you set the sensitivity with the pumps on and then cycle for brake...saw them on a hostital York chiller MER job never again...swetting flow switch is always fun on the chiller side

The Yorkies definitely know more about this than me, but I think they have been using the electronic flow sensors for a little while. We also have a hospital we take care of with a bunch of big YK's and they all have it. I have also seen some air handlers that measure return and outside airflow using these sensors.

I think the term they are using for them is "thermal dispersion sensor". I could be wrong, but as I understand it, there's a heater in the probe, and the controller keeps track of the heater temperature and the heat loss from the probe. It compares the two and determines whether flow is present.

There are lots of different scenarios where a pump could be dead-heading without someone physically closing the discharge valve. If you're trying to prove flow through a heat exchanger, the only way to do it with a DP is with the differential across the heat exchanger.